Abstract:Clays are chosen in Italy and Belgium and considered in the USA and UK as a medium for the isolation of high-level radioactive waste. Very low permeability and high ductility make clay an attractive candidate rock insuring both negligible migration of natural water and ions and sealing of possible fractures and left underground workings. However, the heat of decay of nuclear material causes water pressure to locally increase, generating hydraulic gradient and clay skeleton to yield, possibly affecting soil permeability. Experiments, theory and preliminary numerical simulations are developed in order to elaborate design principles avoiding the adverse effect of heat and exploiting it when possible